<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        *{
            margin: 0;
            padding: 0;

        }
        html,body{
            width: 100%;
            height: 100%;
        }
        header,footer{
            background-color: rgb(180, 178, 178);
            height: 100px;
            clear: both;
        }
        .content{
            padding-left:300px;
            padding-right: 200px;
        }
        .column{
            float: left;
            height: 300px;
        }
        .left{
            width: 300px;
            background-color: aqua;
            /* 定位到首行padding处 */
            margin-left: -100%;
            /* 再向左移动300px */
            position: relative;
            left: -300px;
            /* 或者right：300px */

        }
        .right{
            width: 200px;
            background-color: aquamarine;
            /* 表示没有了宽度，自然就不会被挤下去了 */
            margin-right: -200px;
        }
        .center{
            width: 100%;
            background-color: bisque;
        }

    </style>
</head>
<body>

    <header >头部</header>
    <div class="content">
        <div class="column center">中间</div>
        <div class="column left">左边</div>
        <div class="column right">右边</div>
    </div>
    <footer>尾部</footer>
</body>
</html>